Pain expert Dr. Scott Fishman answers questions about nerve pain:

Q: Why are blood pressure medications recommended for Complex Regional Pain (also known as Reflex Sympathetic Dystrophy or RSD)?

A: Complex Regional Pain Syndrome (CRPS) is a nerve-injury pain that is sometimes mistaken for repetitive soft-tissue strain, a hairline fracture, an infection, a trapped nerve, fascitis, or bone spurs. Its symptoms include redness and swelling, a sudden change in skin color and temperature from red hot to cool blue, and a constant burning that is sometimes accompanied by a jolt of electricity. This disease involves a specific part of the nervous system called the sympathetic system. The sympathetic system is responsible for functions such as heart rate, sweating, changes in skin temperature, as well as blood pressure. Thus, medications that control blood pressure can help with this type of pain.

CRPS can be a chameleon, quickly flaring up and dying down, revealing only one or two of its characteristic symptoms rather than its full spectrum of symptoms. In some patients, the disease causes hair loss along the affected limb; in others it stimulates hair growth. Similarly, a patient's skin may be warmer or cooler than normal.

Early treatment has the best chance for success with CRPS. When the problem has lingered, it is rare that a single nerve block can defeat it. Often, treatment entails a series of injections, and even with this approach, I am never surprised if the pain returns.

The sympathetic nervous system can be calmed with drugs that often are used to treat other conditions that involve these special nerves. If you take medication for high blood pressure, you will recognize the names of many of the drugs given to manage CRPS. Clonidine is one of the common drugs used, as well as the oral forms of phenoxybenzamine and propranolol and many other drugs used for hypertension.

But such drugs raise pros and cons that patients have to weigh. They circulate throughout the body, cooling pain wherever it flares, while possibly producing side effects such as low blood pressure, a slowing or racing heart, sexual dysfunction, and diarrhea.

If turning off the sympathetic nervous system with blood pressure medication doesn't win the battle against the burning, swelling and electric shocks, I look elsewhere for vulnerable inroads to apply treatment. I treat the pain of CRPS like any other form of nerve injury. Since neuropathic pain arises from convulsions or seizures somewhere along nerve pathways, the best weapons are anti-convulsant or anti-seizure medications.

There is no clear research yet to guide me as to which drug to prescribe first, so I usually start with the safest. Neurontin (gabapentin), a relatively new epilepsy drug, is one of the first medications I reach for when I'm expanding pharmacological treatment. It is well tolerated by most patients and has the least possibility of reacting badly with other medicines.

Many other anti-convulsants and anti-arrhythmics can be used with benefit, including mexiletine (Mexitil), generic name (Dilantin), topiramate (Topomax), carbamazepine (Tegretol), lamotrigine (Lamictal), as well as tricyclic antidepressants (Elavil, Tofranil, notriptyline, Desipramine) and others.